1. Field of the Invention
The present invention generally relates to a color filter substrate suitable for use in display devices in which a multi- or full-color display is conducted by combinations of lighting of individual colors, and a liquid crystal color display device using such a filter substrate, and particularly to a liquid crystal color display device in which a multi- or full-color display is conducted by combinations of lighting of four colors of red, blue, green and white.
2. Related Background Art
Various liquid crystal color display devices, which conduct a color display, have heretofore been proposed. As a general device thereof, there is a display device in which one pixel is formed by 3 dots which display 3 colors of red (R), blue (B) and green (G), respectively, and the color display is conducted within the limit of eight colors by combinations of on-off of these dots.
However, in recent years, there has been a strong demand for improvement in the quality of the color display, and so it has been desired that a liquid crystal color display device which can display still more colors be developed. FIG. 1 illustrates an example of such a display device. This liquid crystal color display device 1 is equipped with four color units 2R, 2B, 2G and 2W. These color units 2R, 2B, 2G and 2W are so constructed that filters for red, blue, green and white colors are arranged on a base of the device to display the respective colors. They are also so constructed that in addition to the above-described 8 colors, intermediate colors thereof can also be displayed by combinations of lighting or not lighting, i.e., on or off, of these color units 2R, 2B, 2G and 2W.
These filters for the respective colors are formed by patterning on a base making up the device in accordance with a photolithgraphic process. Since only a filter for one color can be formed by one photolithgraphic step, the photolithographic step has been repeated 4 times for the production of a color filter substrate. Photosensitive resins in which respective colorants were dispersed have been used for the formation of the filters for red, blue and green colors (hereinafter referred to as red filter, blue filter and green filter, respectively), while a photosensitive resin in which no colorant was dispersed has been used for the formation of a filter for a white color (hereinafter referred to as a white filer).
Since the white filter is formed by the photosensitive resin in which no colorant has been dispersed, as described above, its in-plane film-thickness distribution characteristics greatly differ from the other color filters. As a result, the film thickness in every dot of the white filter obtained after the patterning becomes uneven, and so a difference in film thickness between the white filter and the other color filters reaches about 1,500 to 2,000 .ANG., and a great difference in level arises within one pixel in the surface on the liquid crystal side of a color filter substrate, resulting in failure to flatten. For this reason, the alignment behavior of a liquid crystal becomes uneven within one pixel in a liquid crystal color display device, and the drive margin is lowered. In a liquid crystal display device in which a distance (gap) between opposite substrates is small, such as, for example, a display device using a ferroelectric liquid crystal, that problem has been marked.
In addition, the above prior art technique requires to carry out patterning 4 times according to the respective colors of the filters. Therefore, there has been a problem that the production process is complicated compared with the formation of the color filter substrate composed of 3 colors, and so material cost and production cost also increase.